Crystals of both the nNOS and iNOS heme domains are obtained in our lab. The unit cells were found rather large with the longest cell edge of 230-240 E. This poses problems in collection data beyond 3.5 E resolution in-house. Heavy dependence on the synchrotron x-ray facility at SSRL for data collections is expected for both native and heavy atom derivative crystals. MAD phasing techniques will be also attempted.